On Countable Additivity:

- Papineau, Chapter 2 of Philosophical Devices (denumerable=countable)
- Skyrms, Zeno's Paradox of Measure
- Skyms, On Infinitesimals
- Hajek, What Conditional Probability Could Not Be (on the Ratio Formula and infinite sets, among other things)
- Williamson, How Probable is an Infinite Sequence of Heads? (on using infinitesimals for probabilities)
- Easwaran, Regularity and Hyperreal Credences (a really excellent piece that'll give you a sense of the pros and cons of using infinitesimals to do various things)
- Easwaran, Why Countable Additivity?
- Bartha, Countable Additivity and the de Finetti Lottery

On Jeffrey Conditionalization (it is worth noting there are also a number of papers discussing the possibility of a dutch book defense of Jeffrey conditionalization):

- Jeffrey, Probable Knowledge - this can be found in the volume
*Probability and the Art of Judgment*which has a number of papers by Jeffrey about the "Radical Probabilism" view - Field, A Note on Jeffrey Conditionalization
- Garber, Discussion: Field and Jeffrey Conditionalization
- Diaconis and Zabell, Updating Subjective Probability (statistics paper proving various theorems about Jeffrey Conditionalization)
- For van Fraassen's "Judy Benjamin" case in which Jeffrey Conditionalization comes up short, see his "A Problem for Relative Information Minimizers in Probability Kinematics"
- Weisberg, "Commutativity or Holism? A Dilemma for Conditionalizers" (on an interesting problem for Jeffrey Conditionalization).